Growable integer array in Java
A growable int array
The following code implements a growable array.
It uses a real array as the backend. Whenever the array
need more space it just create a new array with double size
and uses the System.copyarray to copy old array
to new array.
public class Main{
public static void main(String[] args) {
IntList list = new IntList();
for(int i=0;i<15;i++){
list.add(i);//from www. j a v a 2s . com
}
System.out.println(list.size());
}
}
class IntList {
private static final int DEFAULT_SIZE = 10;
private int[] data = new int[DEFAULT_SIZE];
private int numElements;
public void add(int f) {
if (numElements == data.length) {
resize(1 + numElements);
}
data[numElements++] = f;
assert numElements <= data.length;
}
public int size() {
return numElements;
}
public int get(int index) {
if (index >= numElements) {
throw new ArrayIndexOutOfBoundsException(index);
}
return data[index];
}
public void put(int index, int val) {
if (index >= numElements) {
throw new ArrayIndexOutOfBoundsException(index);
}
data[index] = val;
}
public void trim() {
if (data.length > numElements) {
int[] newData = new int[numElements];
System.arraycopy(data, 0, newData, 0, numElements);
data = newData;
}
}
public int[] getData() {
return data;
}
private void resize(int minCapacity) {
int newCapacity = 2 * data.length;
if (newCapacity == 0) {
newCapacity = DEFAULT_SIZE;
}
if (newCapacity < minCapacity) {
newCapacity = minCapacity;
}
int[] newData = new int[newCapacity];
System.arraycopy(data, 0, newData, 0, data.length);
data = newData;
}
}
The code above generates the following result.
From the code we can see that the initial size of the list is 10 and we use
the for loop in the Main class to insert 15 elements.
The final size of the list is 15 which is enlarged automatically.